Elliptical element for blood pressure reduction

ABSTRACT

Apparatus is provided for treating hypertension of a subject. The apparatus includes an implantable element which has a non-circular shape and which is configured to reduce the hypertension by facilitating an assumption of a non-circular shape by a blood vessel in a vicinity of a baroreceptor of the subject, during diastole of the subject. Other embodiments are also described.

CROSS-REFERENCE

The present patent application is a continuation of U.S. applicationSer. No. 11/881,256, filed Jul. 25, 2007, entitled “Elliptical elementfor blood pressure reduction”, now U.S. Pat. No. 8,923,972, whichapplication is a continuation-in-part of International PatentApplication PCT/IL2006/000856 to Gross (WO 07/013065), filed Jul. 25,2006, entitled “Electrical stimulation of blood vessels,” which claimsthe benefit of (a) U.S. Provisional Application 60/702,491, filed Jul.25, 2005, entitled, “Electrical stimulation of blood vessels,” and (b)U.S. Provisional Application 60/721,728, filed Sep. 28, 2005, entitled,“Electrical stimulation of blood vessels.” All of the above applicationsare incorporated herein by reference.

FIELD OF THE INVENTION

The present invention generally relates to implanted medical apparatus.Specifically, the present invention relates to apparatus and methods forreducing blood pressure

BACKGROUND OF THE INVENTION

Hypertension is a condition from which many people suffer. It describesa constant state of elevated blood pressure which can be caused by anumber of factors, for example, genetics, obesity or diet. Baroreceptorslocated in the walls of blood vessels act to regulate blood pressure.They do so by sending information to the central nervous system (CNS)regarding the extent to which the blood vessel walls are stretched bythe pressure of the blood flowing therethrough. In response to thesesignals, the CNS adjusts certain parameters so as to maintain a stableblood pressure.

US Patent Application Publication 2003/0060858 to Kieval et al., whichis incorporated herein by reference, describes devices, systems andmethods by which the blood pressure, nervous system activity, andneurohormonal activity may be selectively and controllably reduced byactivating baroreceptors. A baroreceptor activation device is positionednear a baroreceptor, for example a baroreceptor in the carotid sinus. Acontrol system may be used to modulate the baroreceptor activationdevice. The control system may utilize an algorithm defining a stimulusregimen which promotes long term efficacy and reduces powerrequirements/consumption.

US Patent Application Publication 2005/0154418 to Kieval et al., whichis incorporated herein by reference, describes systems and methods toprovide baroreflex activation to treat or reduce pain and/or to cause orenhance sedation or sleep. Methods involve activating the baroreflexsystem to provide pain reduction, sedation, improved sleep or somecombination thereof. Systems include at least one baroreflex activationdevice, at least one sensor for sensing physiological activity of thepatient, and a processor coupled with the baroreflex activationdevice(s) and the sensor(s) for processing sensed data received from thesensor and for activating the baroreflex activation device. In someembodiments, the system is described as being fully implantable within apatient, such as in an intravascular, extravascular or intramurallocation.

US Patent Application Publication 2006/0074453 to Kieval et al., whichis incorporated herein by reference, describes a method for treatingheart failure in a patient which involves activating a baroreflex systemof the patient with at least one baroreflex activation device andresynchronizing the patient's heart with a cardiac resynchronizationdevice. Activating the baroreflex system and resynchronizing the heartmay be performed simultaneously or sequentially, in various embodiments.In some embodiments, one or more patient conditions are sensed and suchcondition(s) may be used for setting and/or modifying the baroreflexactivation and/or heart resynchronization. A device for treating heartfailure includes a baroreflex activation member coupled with a cardiacresynchronization member. Some embodiments further include one or moresensors and a processor. In some embodiments, the device is fullyimplantable.

US Patent Application Publication 2005/0027346 to Arkusz et al., whichis incorporated herein by reference, describes a tubular vascular stentgraft with a passively pulsating midsection where the difference betweenthe cross-sectional areas of the lumen under the systolic and diastolicpressures after the implantation is 10% or more. The pulsating stentgraft accumulates blood during the systolic pressure wave thus loweringthe peak value of the tugging force at the proximal attachment site.

PCT Publication WO 03/076008 to Shalev, which is incorporated herein byreference, describes an implantable device which uses the carotidbaroreflex in order to control systemic blood pressure. The implantincludes sampling and pulse stimulation electrodes preferably located onthe carotid sinus nerve branch of the glossopharyngeal nerve, adjacentand distal to the carotid sinus baroreceptors. The stimulators have anexternal control unit, which communicates with the implant fordetermining appropriate operational parameters, and for retrievingtelemetry information from the device's data bank. Typically, twointernal devices are implanted, one at each side of the patient's neck.

PCT Publication WO 04/073484 to Gross et al., which is incorporatedherein by reference, describes apparatus which includes an inflatablebladder, adapted to be coupled to a blood vessel of a subject carryingoxygenated blood, such that an interior of the bladder is in fluidcommunication with the blood. The apparatus also includes a piston inmechanical communication with the bladder; a motor, adapted tosynchronize contraction and expansion of the bladder with a cardiaccycle of the subject by applying a motor force to the piston; and aspring, adapted to apply a spring force to the piston. In someembodiments of the invention, a counterpulsation system comprises one ormore springs, which are adapted to be inserted into an artery of asubject, such as a descending aorta. Typically, each of the springs isplanar, i.e., flat rather than helical, and has a generally sinusoidalshape. For applications comprising more than one spring, the pluralityof springs are arranged in substantially a single plane. Thecounterpulsation system causes the artery to have a cross-sectional areaduring diastole that is less than the cross-sectional area would beduring diastole without use of the counterpulsation system. For example,the counterpulsation system may cause the artery to have across-sectional shape during diastole that generally resembles anellipse. Use of the counterpulsation system is described as thustypically increasing diastolic blood pressure and decreasing systolicblood pressure, thereby providing counterpulsation treatment to thecirculation of the subject.

CVRx (Minneapolis, Minn.) manufactures the CVRx® Rheos BaroreflexHypertension Therapy System, an implantable medical device for treatingpatients with high blood pressure. The product, which is under clinicalinvestigation, works by electrically activating the baroreceptors, thesensors that regulate blood pressure. These baroreceptors are located onthe carotid artery and in the carotid sinus. CVRx states that when thebaroreceptors are activated by the Rheos System, signals are sent to thecentral nervous system and interpreted as a rise in blood pressure. Thebrain works to counteract this perceived rise in blood pressure bysending signals to other parts of the body to reduce blood pressure,including the heart, kidneys and blood vessels.

The following patents and patent applications, which are incorporatedherein by reference, may be of interest:

US Patent Application Publication 2005/0033407 to Weber et al.

European Patent 0,791,341 to Demeyere et al.

PCT Publication WO 06/032902 to Caro et al.

U.S. Pat. No. 7,044,981 to Liu et al.

US Patent Application Publication 2005/0203610 to Tzeng

US Patent Application Publication 2004/0193092 to Deal

U.S. Pat. No. 6,575,994 to Marin et al.

US Patent Application Publication 2005/0232965 to Falotico

US Patent Application Publication 2004/0106976 to Bailey et al.

U.S. Pat. No. 4,938,766, to Jarvik

U.S. Pat. No. 4,201,219 to Bozal Gonzalez

U.S. Pat. No. 3,650,277 to Sjostrand et al.

U.S. Pat. No. 4,791,931 to Slate

SUMMARY OF THE INVENTION

As people age, their blood vessels become more rigid, and, as a result,the baroreceptor response to changes in blood pressure decreases. TheCNS interprets the low baroreceptor response as resulting from a lowblood pressure, and responds by increasing blood pressure. Thisphenomenon can cause or exacerbate hypertension. Embodiments of thepresent invention reduce hypertension by increasing the changes in shapeof given arteries during the cardiac cycle. Doing so increases thebaroreceptor signaling to the CNS, and the CNS interprets the increasedbaroreceptor signaling as having resulted from elevated blood pressure.In response, the CNS acts to lower blood pressure.

In some embodiments of the present invention, an element having anelliptical or other non-circular cross-section is placed near abaroreceptor in a blood vessel of a subject who has hypertension. Theelliptical element changes the shape of the blood vessel such that theblood vessel is generally elliptical during diastole and less elliptical(e.g., generally circular) during systole.

In some embodiments of the invention, the non-circular element comprisesa stent. Alternatively or additionally, the non-circular elementcomprises a ring, or a plurality of rings. For some applications, theone or more rings are used as the non-circular element in order toreduce the total surface contact between the element and the bloodvessel, which, in turn, limits fibrosis between the element and theblood vessel. Alternatively, as when the element comprises a stent, thecontact surface area is not necessarily minimized, and the one or morerings are used as the non-circular element for a different purpose.

In an embodiment, the ring is flexible and flexes in coordination withthe cardiac cycle of the subject. In a further embodiment, a controlunit is configured to detect the real-time blood pressure of the subjectand to drive current, via the element, toward the baroreceptor,responsively to the detected blood pressure. Alternatively oradditionally, the apparatus comprises a dedicated electrode, and currentis driven toward the baroreceptor, via the dedicated electrode,responsively to the detected blood pressure.

In an embodiment, the cross-section of the ring is altered in responseto the detection of real-time blood pressure of the subject. Forexample, if the blood pressure of the subject increases as a result ofthe subject undergoing a stressful experience, a blood pressure detectordetects the increase. The detected increase in blood pressure results inthe eccentricity of the ring being increased.

In some patients, the baroreceptor adapts to the presence of the ringwithin the blood vessel, and reverts toward its original firing rate. Insome embodiments of the invention, the eccentricity of the ring ismodified periodically, in response to measurements of resting bloodpressure of the subject. For example, a balloon may be transcatheterallyinserted into the inside of the ring. The balloon is inflated to modifythe cross-section of the ring.

In some embodiments, an embolic protection device is inserted into theblood vessel during the implantation of the non-circular element.Typically, the embolic protection device comprises a mesh, and the meshis placed distal to the non-circular element. The mesh is typicallyinserted into the blood vessel transcatheterally.

There is therefore provided, in accordance with an embodiment of theinvention, apparatus for treating hypertension of a subject, includingan implantable element which has a non-circular shape and which isconfigured to reduce the hypertension by facilitating an assumption of anon-circular shape by a blood vessel in a vicinity of a baroreceptor ofthe subject, during diastole of the subject.

In an embodiment, the element includes a non-circular stent.

In an embodiment, the element includes a single non-circular ring.

In an embodiment, the element includes a plurality of non-circularrings.

In an embodiment, the element includes a plurality of non-circular ringswhich are not connected to each other.

In an embodiment, the element includes a plurality of non-circular ringswhich are not rigidly connected to each other.

In an embodiment, the element is rigid.

In an embodiment, the apparatus includes a control unit configured todetect real-time blood pressure of the subject.

In an embodiment, the control unit is configured to be implantable in abody of the subject.

In an embodiment, the control unit is configured to drive current, viathe element, toward the baroreceptor, in response to the detected bloodpressure.

In an embodiment, the apparatus includes an electrode, and the controlunit is configured to drive current, via the electrode, toward thebaroreceptor, in response to the detected blood pressure.

In an embodiment, the control unit is configured to change thecross-section of the element in response to the detected blood pressure.

In an embodiment, the element includes a plurality of rings which arecoupled to each other.

In an embodiment, the apparatus includes a single rod, and the rings arecoupled to each other by the single rod.

In an embodiment, the apparatus includes exactly two rods, and the ringsare coupled to each other by the exactly two rods.

In an embodiment, the apparatus includes three or more rods, and therings are coupled to each other by the three or more rods.

In an embodiment, the element includes two rings which are coupled toeach other and which are separated from each other by a distance that isbetween 5 mm and 20 mm.

In an embodiment, the element includes two rings which are coupled toeach other and which are separated from each other by a distance that isbetween 20 mm and 50 mm.

In an embodiment, the element is flexible.

In an embodiment, the element is configured to flex in coordination witha cardiac cycle of the subject.

In an embodiment, the element is configured to flex passively incoordination with the cardiac cycle of the subject.

In an embodiment, the apparatus includes a control unit configured todetect the cardiac cycle of the subject and to flex the element incoordination with the cardiac cycle.

In an embodiment, the apparatus includes a shaping element configured toshape the non-circular element while the non-circular element is in theblood vessel.

In an embodiment, the shaping element includes a balloon.

In an embodiment, the shaping element includes an elliptical balloon.

In an embodiment, the apparatus includes an embolic protection deviceconfigured to capture emboli during implanting of the element.

In an embodiment, the embolic protection device includes a mesh.

There is additionally provided, in accordance with an embodiment of theinvention, a method for reducing hypertension of a subject, including:

coupling an element having a non-circular cross-section to a bloodvessel of the subject in a vicinity of a baroreceptor of the subject, byimplanting the element; and

reducing the hypertension by facilitating, with the element, anassumption of a non-circular shape by the blood vessel in the vicinity,during diastole of the subject.

In an embodiment, implanting the element includes implanting in separateimplantation steps, at respective longitudinal sites of the blood vesselin the vicinity of the baroreceptor, a plurality of rings havingnon-circular cross-sections.

In an embodiment, implanting the element includes implanting, atrespective longitudinal sites of the blood vessel in the vicinity of thebaroreceptor, a plurality of rings which are coupled to each other, therings having non-circular cross-sections.

In an embodiment, implanting the element includes implanting the elementduring minimally-invasive surgery.

In an embodiment, implanting the element includes placing a stent insidethe blood vessel on one side of the baroreceptor, the stent having anon-circular cross-section.

In an embodiment, implanting the element includes placing a ring insidethe blood vessel on one side of the baroreceptor, the ring having anon-circular cross-section.

In an embodiment, the method includes detecting blood pressure of thesubject and changing the cross-section of the non-circular element inresponse to the detected blood pressure.

In an embodiment, detecting the blood pressure includes detecting theblood pressure of the subject more frequently than once a week.

In an embodiment, detecting the blood pressure includes detecting theblood pressure of the subject less frequently than once a week.

In an embodiment, detecting the blood pressure includes detecting realtime blood pressure of the subject, and changing the cross-section ofthe element includes changing the cross-section of the element inresponse to the detected real time blood pressure.

In an embodiment, detecting the blood pressure includes detectingresting blood pressure of the subject, and changing the cross-section ofthe element includes changing the cross-section of the element inresponse to the detected resting blood pressure.

In an embodiment, changing the cross-section of the element includesexpanding a balloon within the element.

In an embodiment, changing the cross-section of the element includesexpanding an elliptical balloon within the element.

In an embodiment, changing the cross-section of the element includesdriving a current toward the element.

In an embodiment, the element includes first and second rings havingnon-circular cross-sections, and implanting the element includesimplanting the first ring on one side of the baroreceptor and implantingthe second ring on another side of the baroreceptor.

In an embodiment, implanting the first ring and the second ring includesimplanting the first and second rings, the rings not being connected toeach other.

In an embodiment, implanting the first ring and the second ring includesimplanting the first and second rings, the rings not being rigidlyconnected to each other.

In an embodiment, implanting the first ring and the second ring includesimplanting the first and second rings, the rings being coupled to eachother.

In an embodiment, implanting the first ring and the second ring includesimplanting the first and second rings at a longitudinal distance fromeach other that is between 5 mm and 20 mm.

In an embodiment, implanting the first ring and the second ring includesimplanting the first and second rings at a longitudinal distance fromeach other that is between 20 mm and 50 mm.

There is additionally provided, in accordance with an embodiment of theinvention, a method for reducing hypertension of a subject, including:

coupling a ring having a non-circular cross-section to a blood vessel ofthe subject in a vicinity of a baroreceptor of the subject, byimplanting the ring; and

reducing the hypertension by facilitating, with the ring, an assumptionof a non-circular shape by the blood vessel in the vicinity, duringdiastole of the subject.

In some embodiments, implanting the ring includes implanting the ringduring minimally-invasive surgery.

In some embodiments, the ring includes a rigid ring, and implanting thering includes implanting the rigid ring.

In some embodiments, the method includes detecting blood pressure of thesubject and changing the cross-section of the non-circular ring inresponse to the detected blood pressure.

In some embodiments, detecting the blood pressure includes detecting theblood pressure of the subject more frequently than once a week.

In some embodiments, detecting the blood pressure includes detecting theblood pressure of the subject less frequently than once a week.

In some embodiments, detecting the blood pressure includes detectingreal time blood pressure of the subject, and changing the cross-sectionof the ring includes changing the cross-section of the ring in responseto the detected real time blood pressure.

In some embodiments, detecting the blood pressure includes detectingresting blood pressure of the subject, and changing the cross-section ofthe ring includes changing the cross-section of the ring in response tothe detected resting blood pressure.

In some embodiments, changing the cross-section of the ring includesexpanding a balloon within the ring.

In some embodiments, changing the cross-section of the ring includesexpanding an elliptical balloon within the ring.

In some embodiments, changing the cross-section of the ring includesdriving a current toward the ring.

In some embodiments, the ring includes a flexible ring, and implantingthe ring includes implanting the flexible ring.

In some embodiments, the ring is configured to flex in response to acardiac cycle of the subject, and implanting the ring includesimplanting the ring that is configured to flex in response to thecardiac cycle.

In some embodiments, the ring is configured to flex passively incoordination with the cardiac cycle of the subject, and implanting thering includes implanting the ring that is configured to flex passivelyin coordination with the cardiac cycle.

In some embodiments, the ring is coupled to a control unit, the controlunit being configured to detect the cardiac cycle of the subject and toflex the ring in coordination with the cardiac cycle, and implanting thering includes implanting the ring that is coupled to the control unit.

In some embodiments, the method includes detecting real-time bloodpressure of the subject and driving a current toward the baroreceptorresponsively to the detected blood pressure.

In some embodiments, driving the current includes driving the currentvia the ring.

In some embodiments, driving the current includes driving the currentvia an electrode.

In some embodiments, the method includes providing embolic protectionduring the implanting.

In some embodiments, providing the embolic protection includes placing amesh within the blood vessel.

There is additionally provided, in accordance with an embodiment of theinvention, apparatus for treating hypertension of a subject, includingan implantable ring which has a non-circular shape and which isconfigured to reduce the hypertension by facilitating an assumption of anon-circular shape by a blood vessel in a vicinity of a baroreceptor ofthe subject, during diastole of the subject.

In some embodiments, the ring is rigid.

In some embodiments, the apparatus includes a control unit configured todetect real-time blood pressure of the subject.

In some embodiments, the control unit is configured to be implantable ina body of the subject.

In some embodiments, the control unit is configured to drive current,via the ring, toward the baroreceptor, in response to the detected bloodpressure.

In some embodiments, the apparatus includes an electrode, wherein thecontrol unit is configured to drive current, via the electrode, towardthe baroreceptor, in response to the detected blood pressure.

In some embodiments, the control unit is configured to change thecross-section of the ring in response to the detected blood pressure.

In some embodiments, the ring is flexible.

In some embodiments, the ring is configured to flex in coordination witha cardiac cycle of the subject.

In some embodiments, the ring is configured to flex passively incoordination with the cardiac cycle of the subject.

In some embodiments, the apparatus includes a control unit configured todetect the cardiac cycle of the subject and to flex the ring incoordination with the cardiac cycle.

In some embodiments, the apparatus includes a shaping element configuredto shape the non-circular ring while the non-circular ring is in theblood vessel.

In some embodiments, the shaping element includes a balloon.

In some embodiments, the shaping element includes an elliptical balloon.

In some embodiments, the apparatus includes an embolic protection deviceconfigured to capture emboli during implanting of the ring.

In some embodiments, the embolic protection device includes a mesh.

The present invention will be more fully understood from the followingdetailed description of embodiments thereof, taken together with thedrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic illustrations of a non-circular rigidimplant element inside a blood vessel during diastole and duringsystole, respectively, in accordance with an embodiment of the presentinvention;

FIGS. 1C and 1D are schematic illustrations of a non-circular flexibleimplant element inside a blood vessel during diastole and duringsystole, respectively, in accordance with another embodiment of thepresent invention;

FIG. 2 is a schematic illustration of two non-circular rings which arecoupled to each other, in accordance with an embodiment of theinvention;

FIG. 3 is a schematic illustration of two non-circular rings which arecoupled to each other, in accordance with another embodiment of theinvention;

FIGS. 4A and 4B are schematic illustrations of a balloon inside anon-circular ring, the balloon in deflated and inflated states thereof,respectively, in accordance with an embodiment of the present invention;

FIGS. 5A and 5B are schematic illustrations of apparatus for increasingthe rate of firing of a baroreceptor, in accordance with respectiveembodiments of the invention; and

FIG. 6 is a schematic illustration of an implant element having embolicprotection, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Reference is now made to FIGS. 1A and 1B, which are schematicillustrations of a non-circular implant element 20 disposed within ablood vessel 30 of a subject, in accordance with an embodiment of theinvention. Typically, the element is implanted into the aorta or thecarotid artery of the subject. FIG. 1A shows the blood vessel duringdiastole and FIG. 1B shows the blood vessel during systole. Typically,the element includes one or more elliptical rigid rings, and/or anelliptical stent. The element is placed within the blood vessel in thevicinity of a baroreceptor and causes an increase in the change in shapewhich the blood vessel would in any case undergo during the cardiaccycle.

In some embodiments, the element is placed as close as possible to thebaroreceptor, e.g., within 1 cm or 2 cm of the baroreceptor. Theimplanting is typically performed during minimally-invasive surgery,e.g., using a transcatheter approach.

Reference is now made to FIGS. 1C and 1D, which are schematicillustrations of non-circular element 20, in accordance with anotherembodiment of the present invention. In some embodiments (as shown),non-circular element 20 is flexible and flexes passively in coordinationwith the cardiac cycle. Blood vessel 30 changes the shape of element 20from being non-circular during diastole (FIG. 1C), to being morecircular during systole (FIG. 1D). For example, element 20 may begenerally circular during systole, or generally elliptical, with lowereccentricity than during diastole. In all other aspects element 20 isgenerally the same as described hereinabove.

Reference is now made to FIGS. 2 and 3, which are schematicillustrations of implant element 20, comprising two non-circular rings22 and 24, which are coupled to each other by a single rod 26 (FIG. 2)or two or more rods 26 and 28 (FIG. 3), in accordance with respectiveembodiments of the invention. Typically, the width D1 of each of therings is between 2 mm and 6 mm, e.g., 4 mm, and the rings are implantedat a longitudinal separation D2 from each other, along the blood vessel,which is between about 5 mm and 20 mm, or between about 20 mm and 50 mm.During diastole, the ratio of length D4 of the major axis of the ellipseto length D3 of the minor axis is typically between 1.5:1 and 2.5:1,e.g., 2:1. For some applications, the rings are implanted such that onering is disposed within the blood vessel on one side of the baroreceptorand the second ring is disposed within the blood vessel on the otherside of the baroreceptor. In some embodiments, the two rings are notconnected to each other and are implanted in separate implantationsteps. In alternative embodiments, the two rings are coupled to eachother by three or more rods.

Reference is now made to FIGS. 4A and 4B, which are schematicillustrations of a shaping balloon 42, inside non-circular ring 22, inaccordance with an embodiment of the present invention. In FIG. 4A, theballoon is deflated, and in FIG. 4B, the balloon is inflated. In somepatients, baroreceptors adapt to a ring being deployed within a bloodvessel (as described herein) and revert toward their original firingrate. In an embodiment of the invention, periodic measurements are madeof the subject's resting blood pressure. If the blood pressure of thesubject has increased, the eccentricity of the cross-section of the ringis increased by inflation of shaping balloon 42. Typically, the balloonis inserted transcatheterally into the inside of the ring, and theballoon is inflated. The balloon expands and permanently increases theeccentricity of the cross-section of the implanted ring. Alternatively,if it is determined that the eccentricity of the ring is having toogreat an effect on resting blood pressure, the balloon is inflated in amanner to decrease eccentricity (e.g., by increasing the minor axis ofthe ring).

Reference is now made to FIGS. 5A and 5B, which are schematicillustrations of apparatus for increasing the rate of firing of abaroreceptor, in accordance with respective embodiments of theinvention. The apparatus comprises elliptical ring 22, which isimplanted in blood vessel 30, and control unit 52. In FIGS. 5A and 5B,blood vessel 30 is shown during systole. In FIG. 5A the control unit iscoupled to the ring, and in FIG. 5B, the control unit is coupled to anelectrode 54. In some embodiments, the control unit is configured todetect real-time blood pressure of the subject. The control unit isconfigured to drive a current into the blood vessel to excite thebaroreceptor, in a transient manner, in response to real-time bloodpressure measurements. For example, the control unit may detect atransient increase in blood pressure as a result of the subjectundergoing a stressful experience. In response, the control unit excitesthe baroreceptor. The current is typically driven into the blood vesselvia the ring (FIG. 5A) and/or via the electrode (FIG. 51).Alternatively, or additionally, the control unit is configured totransiently modulate the eccentricity of the ring in response to thereal-time blood pressure measurements. For example, the ring maycomprise mechanical deforming elements (e.g., piezoelectric elements),and the control unit actuates the deforming elements to transientlyalter the eccentricity of the ring.

In some embodiments, the ring is flexible, and the control unit isconfigured to detect the cardiac cycle of the subject and to flex thering in coordination with the cardiac cycle, to enhance baroreceptorfiring and blood pressure reduction.

Reference is now made to FIG. 6, which is a schematic illustration of anembolic protection device 60 disposed within the blood vessel duringimplantation of element 20, in accordance with an embodiment of thepresent invention. The implant element and the embolic protection deviceare placed in blood vessel 30 in the vicinity of a baroreceptor.Typically, the embolic protection device comprises a mesh. During theimplanting of the implant element, the embolic protection device isinserted into the blood vessel distal to the implant element. Embolicprotection device 60 is typically inserted into the blood vessel via acatheter 40. The protection device prevents embolisms, caused by theimplanting of the implant element, from occluding blood vessels of thesubject. Following implantation of element 20, embolic protection device60 is removed.

It is to be understood that use of a non-circular plurality of rings isdescribed herein by way of illustration and not limitation, and that thescope of the present invention includes the use of a plurality of ringsthat are circular in cross-section.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present inventionincludes both combinations and subcombinations of the various featuresdescribed hereinabove, as well as variations and modifications thereofthat are not in the prior art, which would occur to persons skilled inthe art upon reading the foregoing description.

What is claimed is:
 1. A method of treating a disease related tohypertension of a subject, the subject having baroreceptors and acentral nervous system responsive to the baroreceptors, comprising:providing a passive flexible element having a non-circularcross-section, the passive flexible element comprising a firstnon-circular flexible end element and a second non-circular flexible endelement, the first non-circular flexible end element coupled to thesecond non-circular flexible end element with three or more rodsextending therebetween, coupling the passive flexible element having thenon-circular cross-section to a carotid artery of the subject in avicinity of the baroreceptors of the subject, by implanting the passiveflexible element within the carotid artery, the passive flexible elementbeing configured to flex passively in coordination with the cardiaccycle; and facilitating, with the passive flexible element, anassumption of a non-circular cross-sectional shape by the carotid arteryin the vicinity that is less circular than a shape of the carotid arteryin the vicinity when the passive flexible element is not coupled to thecarotid artery, wherein passive flexure of the first non-circularflexible end element and the second non-circular flexible end element incoordination with the cardiac cycle of the subject stimulates thebaroreceptors to transmit signals to the central nervous system andtreats the disease related to hypertension.
 2. The method according toclaim 1, further comprising reducing the disease by facilitating, withthe passive flexible element, an assumption of a cross-sectional shapeby the carotid artery in the vicinity, during diastole of the subject,that is less circular than a shape of the carotid artery in thevicinity, during systole of the subject.
 3. The method according toclaim 1, wherein implanting the passive flexible element comprisesplacing the passive flexible element inside the carotid artery on a sideof the baroreceptor selected from the group consisting of: an upstreamside, and a downstream side.
 4. The method according to claim 1, whereinthe passive flexible element is configured to flex passively incoordination with the cardiac cycle of the subject, and whereinfacilitating the assumption of the shape, during diastole, comprises,subsequent to implanting the passive flexible element, allowing thepassive flexible element to flex passively in coordination with thecardiac cycle.
 5. The method according to claim 1, wherein implantingthe passive flexible element comprises coupling the first non-circularflexible end element and the second non-circular flexible end element tothe carotid artery at a longitudinal separation from each other, thenon-circular flexible end elements having non-circular cross-sections.6. The method according to claim 5, wherein coupling the firstnon-circular flexible end element and the second non-circular flexibleend element to the carotid artery comprises longitudinally spacing thefirst non-circular flexible end element and the second non-circularflexible end element by between 5 mm and 20 mm.
 7. The method accordingto claim 5, wherein coupling the first non-circular flexible end elementand the second non-circular flexible end element to the carotid arterycomprises longitudinally spacing the first non-circular flexible endelement and the second non-circular flexible end element by between 20mm and 50 mm.
 8. The method according to claim 1 wherein implanting thefirst non-circular flexible end element and the second non-circularflexible end element comprises implanting the first non-circularflexible end element on a first side of the baroreceptor and implantingthe second non-circular flexible end element on a second side of thebaroreceptor, the first and second sides being respective sides selectedfrom the group consisting of: an upstream side and a downstream side. 9.The method of claim 1, further comprising: increasing flexibility of thecarotid artery in the vicinity of the baroreceptor by removing plaquefrom the carotid artery; wherein the passive flexible element having thenon-circular cross-section is coupled to the carotid artery subsequentlyto removing the plaque.